In grasping a workpiece by using a retracting chuck, jaws are firstly brought close to the workpiece in a radial direction, and grasp the workpiece loosely. Then, the jaws are moved axially within a limited range. During this period, the workpiece is surely seated on a closed contact seat. Then, the workpiece is eventually grasped by moving the jaws in the radial direction. The reason for grasping the workpiece loosely is to closely adhere the workpiece on the closed contact seat by abutting even if the workpiece is inclined.
A body is divided into a moving body and a rear body which are fixed on a spindle through a back plate. The moving body is movable axially relative to the rear body by a plunger and a guide portion of the rear body. The jaws are provided to the moving body side. The rear body and the moving body are connected by a spring. The spring is deflected by cylinder thrust applied on the plunger after the jaws contact the workpiece. According to this, the moving body is drawn axially, and the workpiece is loosely grasped with a cushion property of the spring. In the case of grasping the workpiece finally, the moving body is further drawn in. For example, patent literature 1 and patent literature 2 disclose retracting chucks thus constituted, respectively.